This invention relates to adjustable clamps and methods for controlling the rate of fluid flow through flexible plastic tubing such as used for intravenous infusion of liquid nourishment and/or medication. The intravenous infusion of medicinal fluids is quite common in current medical practice. Anesthetics are infused intravenously during operations, and intravenous feeding is commonly employed in the post-operative period. In addition, there are many patients whose illness either restricts their ability to take food orally or to digest food properly so taken, and then patients must be fed intravenously for the duration of their illness.
The apparatus commonly employed for intravenous infusions includes a stand for supporting a bottle of the appropriate fluid in an elevated position above the patient. A flexible plastic tube is coupled to the bottle for conducting the fluid from the bottle to the patient by a gravity feed. A needle on the end of the flexible tube is inserted into one of the patient's veins, and an adjustable clamp on the tubing is used for controlling the flow rate of the fluid by controlling the cross sectional area of the tubing. In order to measure the flow rate with these devices it is necessary to count visually the number of drops per minute by watching the drops in a drip chamber.
In the past, a problem has been encountered in maintaining a constant fluid flow rate through the flexible plastic tubing (usually polyvinylchloride) because of its physical characteristics. After the desired fluid flow rate has been set with the adjustable clamp, as by restricting a portion of the cross-section of the tubing, the plastic wall of the tubing nevertheless tends to deform or displace slowly resulting in a progressive change in the cross sectional area through which the fluid is flowing, thereby progressively changing the fluid flow rate through the tubing. This requires frequent readjustment of the clamp in order to make sure that the correct fluid flow rate is maintained. Tests have shown that the standard intravenous set loses an average of 45% of its initial flow rate in ten minutes if not readjusted.